In this video, Professor Scott Denning of the Atmospheric Science Department at Colorado State University explains how greenhouse gases in Earth's atmosphere warm our planet. In this lively, animated presentation, Professor Denning first explains how visible light (a form of electromagnetic radiation) from the Sun delivers energy to Earth. Next, he describes how some of this energy is trapped in Earth's atmosphere by the greenhouse effect, which warms our planet. Molecules of greenhouse gases, especially water vapor and carbon dioxide, "recycle" some of the heat energy which would otherwise escape from Earth in the form of infrared radiation.

Most of the gas molecules in our atmosphere are nitrogen (N2) and oxygen (O2). Each of these types of molecules has just two atoms. This means these molecules can only vibrate in one way, and therefore aren't very good at absorbing energy. Carbon dioxide (CO2) and water vapor (H2O) molecules, on the other hand, have three atoms per molecule... so they can vibrate in various different ways. This makes them better at absorbing energy from infrared radiation... which is why they are such effective greenhouse gases.

Adding extra carbon dioxide to Earth's atmosphere increases the temperature of the atmosphere. Humans have added lots of CO2 to the atmosphere, mostly by burning fossil fuels such as oil, coal, and natural gas. This extra CO2 enhances the greenhouse effect and is the main cause of global warming.